Fiber optic sensors system

ABSTRACT

A fiber optic system including a plurality of optical sensors, each with an identification system is disclosed. The fiber optic system includes a fiber, a demodulator, and at least one coupler, optical sensor and corresponding identification system. The identification system is powered by light shunted from the fiber by the coupler to a modulating device. The modulating device modulates the light and transmits it to a power converting device, which transforms the light energy into electrical energy. The electrical energy powers a high temperature integrated circuit upon which is stored a digital identification of a respective optical sensor. The integrated circuit, upon being powered up, sends a modulated response back up to the surface through the modulating device. Alternatively, a passive identification system is described, wherein identification information for a sensor is encoded onto the optical beam as it passes through reflective devices along the length of the fiber.

FIELD OF THE INVENTION

The invention generally relates to fiber optic sensors, and moreparticularly to a fiber optic sensor identification system.

BACKGROUND OF THE INVENTION

Available electronic sensors measure a variety of values, such as, pH,color, temperature, or pressure, to name a few. For systems that requirea string of electronic sensors over a long distance, e.g., twenty tothirty kilometers or longer, powering the electronic sensors becomesdifficult. Conventionally, the powering of electronic sensors requiresrunning electrical wire from a power source to each of the electronicsensors. However, electric wires spanning such long distances create toomuch interference and noise, thereby reducing the accuracy of theelectronic sensors.

Optical fibers have become the communication medium of choice for longdistance communication due to their excellent light transmissioncharacteristics over long distances and the ability to fabricate suchfibers in lengths of many kilometers. Further, the light beingcommunicated can also power the sensors, thus obviating the need forlengthy amounts of electric wire. This is particularly important in thepetroleum and gas industry, where strings of electronic sensors are usedin wells to monitor down hole conditions. Powering electronic sensorselectrically has been a problem in the petroleum and gas industry.

As a result, in the petroleum and gas industry, fiber optic sensors areused to obtain various down hole measurements, such as, pressure ortemperature. A string of optical fibers within a fiber optic system isused to communicate information from wells being drilled, as well asfrom completed wells.

Conventionally, each sensor in a multi-sensor fiber optic system iscalibrated to a particular communication channel. Thus, each sensorsends data back to a dedicated communication channel. Currently,calibration coefficients for each communication channel, which arenecessary to ensure that data from a particular sensor is communicatedto the proper channel, are manually entered. If a particular channel isdefective or, for whatever reason, cannot be used to receive data, thecalibration coefficients for the respective sensor have to be manuallyre-entered into another channel, increasing the possibility of humanerror.

SUMMARY OF THE INVENTION

The optic sensor system of the present invention includes a sensorconnected to a monitoring apparatus. The sensor is also connected to adedicated identification device. The monitoring apparatus sends anoptical signal to the sensor, and a return optical signal from thesensor includes a unique identifier from the identification device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which form a part of the specification andare to be read in conjunction therewith and in which like referencenumerals are used to indicate like parts in the various views:

FIG. 1 is a schematic view of a fiber optic system having identificationsystems constructed in accordance with an exemplary embodiment of theinvention; and

FIG. 2 is a schematic view of an alternate embodiment of a fiber opticsystem having identification systems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a fiber optic system 10 is shown. System 10includes a monitoring apparatus 50 including a channel array 40 and acentral processing unit 42 in connection with an interrogator 14 locatedat the surface. Preferably, interrogator 14 is a demodulator. A firstfiber 12 extends from demodulator 14 down to a first sensor 18. Alsoillustrated is a second fiber 112 extending down to a second sensor 118.It should be appreciated that the number of fibers 12, 112 extendingdown hole from demodulator 14 is not fixed and is a sufficient number offibers to allow communication between a number of sensors 18, 118 downhole with demodulator 14.

Sensors 18, 118 are each associated with a respective, dedicatedidentification system 20, 120. Identification system 20 includes acoupler 16, a shunt line 22, a modulating device 24, a power convertingdevice 26, and a high temperature integrated circuit 28. Identificationsystem 120 similarly includes a coupler 116, a shunt line 122, amodulating device 124, a power converting device 126, and a hightemperature integrated circuit 128.

Monitoring apparatus 50 may be a standard stationary monitoringapparatus, or it may be a portable monitoring apparatus that istransported from well to well for the purpose of obtaining data fromeach respective well. For example, a portable monitoring apparatus 50may be coupled with a first well, at which relevant data from the well,taken and reported by sensors 18, 118, is obtained. Then, the portablemonitoring apparatus 50 may be decoupled from the first well, moved to asecond well, and coupled with the second well to obtain likeinformation.

After monitoring apparatus 50 has been coupled with a well, it isimportant to ascertain which sensors are associated with which channelin channel array 40. As shown, two channels 40 _(A) and 40 _(B) aredenoted. To ascertain which sensor 18, 118 is associated with whichfiber 12, 112, a signal is sent from demodulator 14 down fiber 12. Thelight signal, travels through fiber 12 to coupler 16, where a majorityof the light continues along fiber 12 to sensor 18. A portion of thelight, such as about ten percent (10%), is shunted off onto fiber opticshunt line 22 toward modulating device 24.

Modulating device 24 may modulate through any suitable mechanism, suchas through electro-optical or microelectromechanical (MEMS) means.Modulating device 24 causes periodic intensity variations in the lightreflected back to demodulator 14 through coupler 16 in response to thelight sent from demodulator 14 to identification system 20. In otherwords, the intensity variations only occur when individual sensor 18 isaddressed. The modulation occurs as a result of changing the propertiesof the optical path. This can be accomplished by inserting a reflectorin the path with a MEMS device or changing the polarization with an LCDdevice.

The light transmitted through shunt line 22 is transmitted throughmodulating device 24 and converted into electrical energy by powerconverting device 26. Alternatively, the light transmitted through shuntline 22 may be transmitted directly to power converting device 26 forconversion into electrical energy. A suitable power converting device 26may be a photocell. Power converting device 26 may include ananti-reflective coating which provides a minimum and constant amount ofreflection to minimize interference with fiber optic sensor 18.

The now converted electric energy powers integrated circuit 28.Information identifying the particular sensor 18 to which identificationsystem 20 is coupled is stored on integrated circuit 28. Integratedcircuit 28 may be a standard high temperature integrated circuit such asthose manufactured by Honeywell and rated to 200° C. for a ten year meantime before failure (MTBF). Alternatively, integrated circuit 28 mayinclude one of various more exotic constructions, such as sapphire ordiamond, which are rated for higher than 200° C. for a ten year MTBF.

The electrical energy, which comes from power converting device 26 tointegrated circuit 28, provides power to integrated circuit 28 to allowit to send the identifying information back to the surface. In responseto the electrical energy, integrated circuit 28 sends a modulatingresponse 30 back to modulating device 24. Modulating response 30 may beas simple as a digital identification number corresponding to relevantsensor 18 or as complex as all the calibration data for relevant sensor18. Modulating device 24 forwards modulating response 30 back throughcoupler 16 and up fiber 12 to demodulator 14 on the surface. Theidentifying information is used to verify that sensor 18 is associatedwith fiber 12 and is calibrated to a particular channel, such as channel40 _(A). A similar exercise is then accomplished with fiber 112 toverify that sensor 118 is associated with fiber 112.

In operation, a light signal is transmitted through fiber 12 bymonitoring apparatus 14 to coupler 16 corresponding with a particularsensor 18 and its respective identification system 20. The signal is foronly a specific sensor, and thus only its respective identificationsystem 20 will be enabled to respond. A portion of the light is shuntedaway from fiber 12 leading to sensor 18 and onto optical fiber shuntline 22. The shunted light passes through modulating device 24, such asa liquid crystal display, which then transmits the light to powerconversion device 26, such as a photocell. Photocell 26 transforms thelight energy into electrical energy and sends the electrical energy inpulses toward the high temperature integrated circuit 28.

Now powered by the electrical energy, and in response to the pulsedsignal provided by photocell 26, integrated circuit 28 sends amodulating response 30 to modulating device 24. Modulating response 30is determined by the digital information contained in integrated circuit28. Integrated circuit 28 does not send any information until the propersequence of pulses is first received from photocell 26. The pulsesequence is a trigger or command for the sensor circuit to send one ormore packets of information. Modulating response 30 is then transmittedback up to the surface.

Alternatively, modulating device 24 may be pre-set to reflect theshunted light at a particular intensity, which intensity correlates to aparticular sensor 18. For example, modulating device 24 may be a digitalmicromirror device (DMD), such as those available from TexasInstruments. While most DMDs are dynamically controlled, i.e., theindividual micromirrors in the array are toggled in real time to drivethe modulation of the optical beam, a DMD may also be passive. In thiscase, the individual micromirrors are set into a particularconfiguration which is not altered thereafter. Central processing unit42 can be pre-programmed to recognize the signature generated by themodulation caused by a particular DMD to identify a particular sensor.For example, central processing unit 42 may contain memory that stores adatabase of signatures and corresponding sensors as well as calibrationdata related to those sensors. By comparing the detected signal to thesignatures in the database, sensor 18 may be identified.

Additionally, the digital information contained in integrated circuit 28can also be stored in central processing unit 42. When the informationidentifying the sensor is stored in the central processing unit 42 orthe monitoring device 50, dedicated channels 40 _(A), 40 _(B) may beomitted. The measurement readings from sensors 18, 118 are continuallycoupled with or are associated with the identifying information, therebyassociating the measurements to the sensor without the need for adedicated channel.

In another embodiment, shown in FIG. 2, a fiber optic system 210 isincludes a monitoring apparatus 250 that includes a channel array 240and a central processing unit 242 at the surface, similar to channelarray 40 and central processing unit 42 discussed above with respect toFIG. 1.

Monitoring apparatus 250 also includes at the surface an interrogator214. Preferably, interrogator 214 is an optical frequency domainreflectometer (hereinafter, “OFDR”). Such devices are known in the art,and OFDRs typically utilize swept-wavelength interferometry tointerrogate systems and/or devices. OFDR 214 may be any OFDR known inthe art, such as those available from Luna Technologies Inc. ofBlacksburg, Va. OFDR 214 includes at least a light source 244 and adetector 246. Although shown in FIG. 2 as separate components,alternatively, OFDR 214 may also incorporate channel array 240 and/orcentral processing unit 242 within a single unit (not shown).

A first fiber 212 connects OFDR 214 to a first sensor 218. Similarly, asecond fiber 312 connects OFDR 214 to a second sensor 318. More sensorsmay be utilized as desired, depending upon the well system to bemonitored. Associated with each sensor 218, 318 is a dedicatedidentification device 220, 320, respectively. For clarity ofdescription, the arrangement of system 210 with respect to sensor 218 isdescribed; the other sensors within system 210 are arranged in a similarmanner.

Identification device 220 is preferably a fiber Bragg grating (FBG),although the use of any reflective medium capable of causing intensityor frequency variations or phase shift within a light beam isappropriate for use with the present invention. Identification device220 is preferably placed in series with sensor 218 on fiber 212. Aswould be apparent to those skilled in the relevant art, identificationdevice 220 may be a separate FBG that is optically coupled with fibers212. Alternatively, identification device 220 may also be writtendirectly into fiber 212, or incorporated into sensor 218. FBGs thatmodulate or reflect light to encode signals are known in the art.

Encoded into identification device 220 is information related to theirrespective associated sensor 218 such as a serial number, calibrationdata, or the like. Preferably, a binary “bit” is written in a specificspatial location in fiber 212. In other words, at a given location alongthe length of fiber 212, a value of one or zero is encoded, where “one”is the presence of a grating pattern or other reflective device and“zero” is the absence of a grating pattern or other reflective device. Aseries of bits at pre-determined locations within fiber 212 contain allof the desired information, such as numbers in a serial code or acalibration coefficient. Each encoded location could be specified to be,for the purposes of example only, 1 cm apart starting at a specificpoint in fiber 212. A series of bits could correspond to a particulardigit in the sensor serial number or calibration coefficient. Any knownbinary coding scheme could be employed.

In operation, OFDR 214 interrogates sensor 218 by passing an opticalsignal through identification device 220 as the light travels to andfrom sensor 218. Both sensor 218 and identification device 220 alter theoptical beam to encode data therewithin. The signal is then reflectedback to OFDR 214, where the signal is detected. In addition to theinformation gathered from sensor 218, OFDR 214 detects the encodedidentification information reflected from identification device 220. Theinformation is then transmitted to central processing unit 242. Centralprocessing unit 242 is programmed with the predetermined bit spacing andformat, and the necessary fiber sensor identification or calibrationinformation can then be extrapolated. Sensor 218 may then be identified,calibrated, and assigned to a specific channel 240 _(A) within channelarray 240. A similar process is performed for sensor 318 usingidentification device 320 to assign sensor to a channel 240 _(B), aswell as any other sensors included with system 210. Alternatively, asthe encoded information from identification device 220, 320 istransmitted with each interrogation, central processing unit 242 may beprogrammed to determine the sensor of origin of the signal with eachinterrogation. In such a case, sensor 218 would not be assigned to adedicated channel.

Alternatively, identification device 220 may be the optical fiber leadto sensor 218. As is known in the art, Rayleigh scattering, thescattering of light by the particles of the material through which thelight is transmitted, occurs in optical fiber transmissions. When sensor218 is manufactured, the unique Rayleigh scattering profile of the leadis scanned with an OFDR. This Rayleigh scattering profile, which remainsfixed throughout the usable life of sensor 218, is recorded and storedin a database in central processing unit 240. Sensor 218 is deployeddown hole by splicing the lead onto fiber 212 or coupling the leadthereto using a mechanical coupler. After sensor 218 is deployed downhole, OFDR 214 interrogates sensor 218 and compares the receivedRayleigh scattering profile with the database, thereby identifying thescanned sensor as sensor 218.

Yet another manner in which the lead to sensor 218 may be used asidentification device 220 is to intentionally vary the length of theleads for all sensors in system 210 in a known fashion. In a typicalmulti-sensor system, care is taken to splice all leads the same lengthand to ensure invisibility of the splice. However, for use asidentification device 220, the splice is intentionally made visible tothe interrogation beam. Using sensor 218 as a reference reflector, thedistance between the splice and sensor 218 is measured. This measurementis then compared with a database of sensor lead lengths stored incentral processing unit 242 in order to identify the scanned sensor assensor 218.

Another alternative for identification device 220 is a spectral filter.OFDR 214 preferably employs a tunable laser as the light source. Thislaser cycles through the available channels at specified increments. Atypical OFDR utilizes hundreds of channels. Identification device 220can remove a pre-determined portion of the channel spectrum, therebyproviding a signature to identify sensor 218.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objectives of the present invention, it isappreciated that numerous modifications and other embodiments may bedevised by those skilled in the art. Additionally, feature(s) and/orelement(s) from any embodiment may be used singly or in combination withother embodiment(s). Therefore, it will be understood that the appendedclaims are intended to cover all such modifications and embodiments,which would come within the spirit and scope of the present invention.

1. An optic sensor system comprising: an optical sensor outputting anoptical signal connected to a monitoring apparatus and an identificationdevice dedicated to the sensor, wherein the optical sensor is capable ofreturning a return optical signal, which includes a unique identifierfrom the identification device when the monitoring apparatus sends aninterrogating optical signal to the optical sensor, wherein theinterrogating optical signal reaches the optical sensor in asubstantially unaltered waveform.
 2. The optic sensor system of claim 1,wherein the identification device is connected in series with thesensor.
 3. The optic sensor system of claim 1, wherein theidentification device comprises a Bragg grating.
 4. The optic sensorsystem of claim 3, wherein the unique identifier comprises a modulatedfrequency of the return optical signal.
 5. The optic sensor system ofclaim 1, wherein the identifier comprises a Rayleigh scattering patternunique to said sensor.
 6. The optic sensor system of claim 5, whereinthe monitoring apparatus stores said unique Rayleigh scattering patternand compares the stored pattern to the pattern associated with thereturn optical signal to identify the sensor.
 7. The optic sensor systemof claim 1, wherein the identification device is connected to the sensorthrough a coupler.
 8. The optic sensor system of claim 7, wherein theidentification device comprises a modulating device that modulates thereturn optical signal at a varied intensity.
 9. The optic sensor systemof claim 7, wherein the identification device comprises an integratedcircuit capable of storing unique information about the sensor.
 10. Theoptic sensor system of claim 9, wherein the integrated circuit ispowered by electrical power converted from at least a portion of theoptical signal.
 11. The optic sensor system of claim 10, wherein theidentification device comprises an optical to electrical powerconverter.
 12. The optic sensor system of claim 9, wherein about 10% ofthe optical signal is shunted off for conversions to electrical power.13. The optic sensor system of claim 8, wherein the modulating devicecomprises a MEMS device.
 14. The optic sensor system of claim 13,wherein the modulating device comprises a DMD.
 15. The optic sensorsystem of claim 1, wherein the monitoring apparatus comprises an opticalfrequency domain reflectometer.
 16. The optic sensor system of claim 15,wherein the identification device comprises several reflective devicesplaced an optical fiber length in series.
 17. The optic sensor system ofclaim 16, wherein the monitoring apparatus is programmed with theanticipated location of the reflective devices along the length of thefiber, and wherein the presence or absence of the reflective device isinterpreted as data related to the sensor.
 18. The optic sensor systemof claim 1, wherein the identification device comprises a spectralfilter.
 19. The optic sensor system of claim 1, wherein the monitoringapparatus is permanently connected to a well.
 20. The optic sensorsystem of claim 1, wherein the monitoring apparatus is removablyconnected to a well.
 21. The optic sensor system of claim 1, wherein theidentification device contains a sensor serial number.
 22. The opticsensor system of claim 1, wherein the identification device containssensor calibration data.
 23. The optic sensor system of claim 1, whereinthe unique identifier comprises a modulated frequency of the returnoptical signal.
 24. The optic sensor system of claim 1, wherein theidentification device comprises a modulating device that modulates thereturn optical signal at a varied intensity.
 25. The optic sensor systemof claim 1, wherein the identification device comprises severalreflective devices placed on an optical fiber length in series.
 26. Theoptic sensor system of claim 25, wherein the monitoring apparatus isprogrammed with the anticipated location of the reflective devices alongthe length of the fiber, and wherein the presence or absence of thereflective device is interpreted as data related to the sensor.
 27. Theoptic sensor system of claim 1, wherein the identification devicecomprises a binary number written on an optical fiber segment.
 28. Theoptic sensor system of claim 1, wherein only one said optical sensor andone said identification device are located on a branch of optical fiber.